Completion procedures for oil and gas wells include lining the drilled hole with a steel casing. The casing is held in place by pumping cement formulations down the casing and upwards into the annular space between the outside surface of the casing and the wall of the wellbore. Typically, successive casing strings are run in progressively smaller diameters as the well is drilled. The number of casing strings used is determined by the drilling engineer to optimize completion costs based on, inter alia, well depth and the geological pressures that must be contained and controlled by the casing strings.
The casing cement between the well casing and the wellbore is designed to set within a certain time period based on the length of time that is required to pump the cement into its desired location and further to allow for anticipated equipment failures and the like. The cement is also designed for utilisation with the temperature and other physical factors associated with the intended location of the well cement.
Cement hardens or sets in a certain period depending on chemical reactions between the cement components. The temperature of the reacting materials is an important parameter and is used to determine the rate at which the reaction takes place. The temperature further is an important factor in determining the physical properties of the solidified cement.
In conducting the drilling and casing operations, a first relative large diameter hold is drilled to a predetermined depth. A steel casing of appropriate diameter is run from the surface to that initial depth. Cement is subsequently pumped down the casing. The cement is followed by a plug which pushes the cement into the well annulus outside the casing string from the bottom of the casing. The cement is then allowed to set. The period of time for the setting to take place is called “waiting for cement” (WOC). During this period the drill rig and the operating crew can do no further work on that well.
When the cement has set and the well passes a pressure test to ensure the cement will hold a specified pressure, the drilling continues. The plug and the residual cement is drilled through within the previously installed casing. When the depth of the next drilling stage is reached, a similar procedure follows and so on until the final desired well depth is reached. In particularly deep wells, there may be four (4) or more successive casing strings, each having an associated waiting period while the cement installed for that casing sets.
The WOC is expensive and disadvantageous. Wells are typically drilled under drilling agreements based on the time required to perform the drilling and casing operations. The deeper the well, the higher the costs which costs increase with the greater size and complexity of the drilling equipment necessary for the deep drilling. In particularly deep offshore wells, for example, the WOC can be twenty-four (24) hours or greater for each casing string. It would be clearly be desirable to reduce this time.
In our recently issued U.S. Pat. No. 6,384,389 (Spencer), the contents of which are incorporated herein by reference and in our co-pending application Ser. No. 10/289,9127, filed Nov. 6, 2002 and entitled DOWNHOLE INDUCTION HEATING TOOL AND METHOD OF USING SAME, the contents of which are also incorporated herein by reference, there is disclosed an induction heating tool that is contemplated to be useful and to overcome some of the aforementioned difficulties in setting cement. A resistive type down hole heating tool offers some advantages.